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P077B Output Speed Sensor Circuit Direction Error

The OBD2 code P077B indicates a malfunction in the output speed sensor circuit, specifically that the sensor is detecting an incorrect direction of the output shaft speed, which may suggest a problem with the...

Definition

The OBD2 code P077B indicates a malfunction in the output speed sensor circuit, specifically that the sensor is detecting an incorrect direction of the output shaft speed, which may suggest a problem with the transmission or sensor itself

Common causes

  • Faulty output speed sensor
  • Wiring issues (shorts, opens, or corrosion)
  • Poor electrical connections
  • Transmission control module (TCM) malfunction
  • Incorrectly installed or damaged transmission components
  • Fluid level or quality issues
  • Mechanical transmission problems
  • Software issues in the TCM

Common misdiagnoses

  • Transmission fluid issues
  • Faulty transmission control module (TCM)
  • Incorrectly installed or damaged output speed sensor
  • Wiring or connector problems
  • Internal transmission failure
  • Faulty input speed sensor
  • Engine control module (ECM) issues
  • Software or calibration errors

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. Addressing any additional codes may help in diagnosing the problem

  2. 2. Inspect Wiring and Connectors

    Visually inspect the wiring and connectors associated with the output speed sensor. Look for signs of damage, corrosion, or loose connections

  3. 3. Ensure that the connectors are securely attached and that there are no bent pins

  4. 4. Test the Output Speed Sensor

    Use a multimeter to test the output speed sensor for proper voltage and resistance according to the manufacturer's specifications

  5. 5. If the sensor is faulty, replace it

  6. 6. Check Transmission Fluid Level and Condition

    Ensure that the transmission fluid is at the correct level and is in good condition. Low or dirty fluid can affect sensor performance

  7. 7. If the fluid is dirty or burnt, consider performing a transmission fluid change

  8. 8. Inspect the Transmission Control Module (TCM)

    Check for any signs of damage or corrosion on the TCM

  9. 9. If necessary, reprogram or replace the TCM if it is determined to be faulty

  10. 10. Check for Mechanical Issues

    Inspect the transmission for any mechanical issues that could affect the output speed sensor's performance, such as worn gears or internal damage

  11. 11. If there are mechanical problems, they may need to be addressed before the code can be cleared

  12. 12. Clear the Codes and Test Drive

    After performing the necessary repairs, clear the trouble codes using the OBD-II scanner

  13. 13. Take the vehicle for a test drive to see if the code returns. Monitor the transmission performance during the drive

  14. 14. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to the P077B code

  15. 15. Seek Professional Help

    If the issue persists after performing the above steps, consider seeking help from a qualified mechanic or transmission specialist who can perform more in-depth diagnostics. By following these troubleshooting steps, you can systematically identify and resolve the issue associated with the P077B code